This invention relates to colloidal size particulates containing particles of a solid, water-insoluble organic material and to polymerization processes used to prepare such particulates.
Metals, metal oxides, pigments, fillers and other inorganic particulates that tend to agglomerate are often coated with or encapsulated in hydrophobic polymers. These coated or encapsulated particles are often used in a wide variety of applications such as electroconductive additives to plastics, toners in electrophotographic applications, pigmented paints as well as many other applications.
Conventionally, such particulates are prepared by (1) treating the inorganic solid with acid, a combination of acid and base, alcohol or a polymer solution; (2) dispersing an addition polymerizable monomer in an aqueous dispersion of a treated inorganic solid and (3) subjecting the resulting dispersion to emulsion polymerization conditions. Examples of such methods are described in U.S. Pat. Nos. 4,048,136; 4,194,920; 3,383,346; 3,935,340; 3,544,500 and 3,884,871. Unfortunately, these methods are deficient in that they often require expensive multi-step procedures, anchoring agents, functional additives, stabilizing agents, and the like. Also, the polymeric particulates often must be employed as viscous pastes or dry powders.
More recently, as disclosed in U.S. Pat. No. 4,049,604, aqueous dispersions of organic polymeric particles are provided by dispensing an oil phase containing emulsion polymerizable monomers in an aqueous phase containing an emulsifier and a sulfo ester containing a polymer, and subjecting the dispersion to emulsion polymerization conditions. The resulting polymeric products are described as microspheres which are useful as coating compositions or microspheres having liquid centers.
Colloidal size inorganic materials have been disclosed as being dispersed in hydrophobic polymers in U.S. Pat. No. 4,421,660. However, the dispersion of organic materials such as organic dyes or pigments in such hydrophobic polymers is not taught or suggested.
In view of the deficiencies of the prior art methods for preparing such particulates, an improved method which eliminates or substantially reduces the adverse effects of the aforementioned procedure deficiencies is highly desirable. In addition, it would be highly desirable to provide a dispersion of colloidal organic materials in hydrophobic polymers.